Title of Work

Are all N2-fixing taxa equal?- Taxon-specific nitrogen-fixation rates of benthic cyanobacteria and diatoms under different environmental conditions

Document Type


Publication/Presentation Date

May 2021

Conference Location



In nitrogen-poor streams or under nitrogen-limiting conditions, algae and cyanobacteria that fix atmospheric nitrogen can have a competitive advantage over other taxa. As an energetically costly process, however, N2-fixation rates can be constrained by light availability and temperature levels. Environmental preferences of different N2-fixing species can further shape distribution patterns over time and space. The abundance and species composition of N2-fixing taxa, and their rates of N2-fixation can determine how, where, and under what conditions nitrogen enters the ecosystem and where it goes from there. From nitrogen-poor streams in Iceland and California, we compared N2-fixation rates for cyanobacteria (e.g., Anabaena, several Nostoc species, Rivularia) and Epithemia spp. (diatoms with cyanobacteria endosymbionts) under different light and temperature conditions. N2-fixation rates varied by genus and species, though light and temperature preferences complicated taxon-specific comparisons. N2-fixation rates generally increased with temperature but varied by taxon. Results highlighted areas needing further research. Knowledge of taxon-specific N2-fixation rates under varied environmental conditions will strengthen our ability to scale up predictions of nitrogen cycling and to predict biofilm response to our warming, nutrient-rich world.